Method and device for producing extreme ultraviolet radiation and soft x-ray radiation

ABSTRACT

A method for generating extreme ultraviolet radiation and soft x-ray radiation with a gas discharge operated on the left branch of the Paschen curve, in particular, for EUV lithography, 
     wherein a discharge chamber ( 10 ) of a predetermined gas pressure and two electrodes ( 11, 12 ) are used, wherein the electrodes have an opening ( 14, 15 ), respectively, positioned on the same symmetry axis ( 13 ) and, in the course of a voltage increase ( 16 ) upon reaching a predetermined ignition voltage (U z ), generate a plasma ( 17 ) located in the area between their openings ( 14, 15 ), which plasma is a source of the radiation ( 17 ′) to be generated,
 
wherein an ignition of the plasma ( 17 ) is realized by affecting the gas pressure and/or by triggering,
 
and wherein, with the ignition of the plasma ( 17 ), an energy storage device supplies by means of the electrodes ( 11, 12 ) stored energy into the plasma ( 17 ), characterized in that the ignition of the plasma ( 17 ) is realized by using a predetermined ignition delay ( 18 ).

BACKGROUND OF THE INVENTION

The invention relates to a method for generating extreme ultravioletradiation and soft x-ray radiation with a gas discharge operated on theleft branch of the Paschen curve, in particular, for EUV lithography,wherein a discharge chamber of a predetermined gas pressure and twoelectrodes are used, wherein the electrodes have an opening,respectively, positioned on the same symmetry axis and, in the course ofa voltage increase upon reaching a predetermined ignition voltagegenerate a plasma located in the area between their openings, whichplasma is a source of the radiation to be generated, wherein an ignitionof the plasma is realized by affecting the gas pressure and/or bytriggering, and wherein, with the ignition of the plasma, an energystorage device supplies by means of the electrodes stored energy intothe plasma.

A method with the aforementioned method steps is known from DE-A-197 53696. The method is carried out in a device comprising an electrodesystem forming the discharge chamber. By means of this electrode system,extreme ultraviolet radiation and soft x-ray radiation are generatedthat can be used, in particular, for EUV lithography. The electrodesystem is comprised of two electrodes, i.e., a cathode and an anode,each having an opening. The opening is essentially a hole, and bothopenings are positioned on a common axis of symmetry. The cathode isembodied as a hollow cathode, i.e., it has a cavity. This cavity is usedin order to generate the electrical field in a predetermined way. Inparticular, the arrangement of the electrodes is such that the fieldlines in the area or the bore holes are sufficiently stretched so thatthe firing condition of above a certain voltage is fulfilled. Thedischarge chamber is filled with gas, and the gas pressure, at least inthe area of the electrode system, is within the range of 1 Pa to 100 Pa.The geometry of the electrodes and the gas pressure are selected suchthat the desired ignition of the plasma is realized on the left branchof the Paschen curve and, as a result of this, no dielectric firingbetween the electrodes outside of the openings occurs. As a result ofthe ignition, a current-conducting plasma channel of axial-symmetricalshape results in the area of the openings of the electrodes. Inaddition, current is supplied by means of the energy storage device viathis channel. The resulting Lorentz force constricts the plasma. As aresult of this constriction effect and because of resistance heating,very high temperatures occur within the plasma and radiation of a veryshort wavelength is generated. The known device can produce EUV light inthe wavelength range of 10–20 nm.

In connection with the method it is important that a switching elementbetween the electrode system and the energy storage device isprincipally not needed. Accordingly, a low-inductive and effectivecoupling of the electrically stored energy into the electrode system canbe achieved. Poles energies of a few Joules are sufficient in order totrigger current pulses in the range of several kilo ampere up to several10 kilo ampere. Triggering of the energy coupling into the dischargethat is operated in a controlled fashion or by automatic firing isrealized by adjustment to a predetermined ignition voltage. The ignitionvoltage is affected, for example, by the gas composition, thetemperature, pre-ionization, electrical field distribution, and otherparameters. It can be adjusted according to the Paschen curve by meansof the gas pressure of the discharge vessel. The energy storage devicemust also be charged up to this ignition voltage in order to be able tosupply in the case of ignition as much energy as possible into theplasma.

The invention has the object to improve a method comprising theaforementioned method steps such that the radiation yield, i.e.,particularly the yield of EUV light, for each pulse is improved as wellas the pulse-to-pulse stability of a plurality of sequentially performeddischarges that are utilized in the method performed with pulseoperation for generating the EUV light.

SUMMARY OF THE INVENTION

The aforementioned object is solved in that the ignition of the plasmais realized by using a predetermined ignition delay.

Carrying out the method with ignition delay results in a prolongation ofthe generation of the conductive plasma. In this way, an improvement ofthe cylinder symmetry of the low-impedance starting plasma that isrequired for discharge is obtained, i.e., of that plasma that isgenerated in the area of the openings of the electrodes after reachingthe ignition voltage. The ignition delay results accordingly in animprovement of the EUV yield/pulse and the pulse-to-pulse stability. Inconnection with the method in a range of pulse operation of 50 Hz to 500Hz an increase of the EUV yield by approximately 10 percent has beenobserved when selecting an ignition delay of approximately 1 ms.

For affecting the ignition delay, the method is carried out such thatthe ignition delay is reduced by increasing the gas pressure or isincreased by reducing the gas pressure. Such changes of the gas pressurecan be obtained particularly easily when the gas flows through the areaof the electrode system, for example, in order to affect the repetitionfrequency, i.e, to thereby perform the method with increased pulsefrequencies.

In order to affect the ignition delay, the method can be performed suchthat the ignition is realized by triggering a triggering pulse which issupplied to a triggering electrode affecting the ignition area of theplasma. By the triggering action, the distribution of the chargecarriers in the ignition area of the plasma is affected and in this wayalso the point in time at which the ignition effectively occurs.

It is expedient to carry out the method such that the triggering actionfor achieving a predetermined ignition delay is carried out incombination with an application of a pressure interval of the gaspressure. In this case, the pressure as well as the point in time oftriggering are adjusted because the discharge, even for a triggeredoperation, can be carried in a stable way, or if at all, only within acertain pressure interval.

In the afore described connection of triggering, the method can becarried out such that triggering is employed together with apredetermined triggering delay. The ignition delay is increasedaccordingly.

The introduction of stored energy into the discharge that is carried outby automatic firing is realized together with the firing, i.e.,automatically with the ignition of the plasma, wherein it should beensured in this connection that the energy storage device taking intoconsideration the pulse operation is charged before the ignition iscarried out. It is therefore necessary to have available information inregard to the voltage increase and obtaining a predetermined ignitionvoltage. As a result of this, the method can be carried out such thatthe voltage increase and/or obtaining a predetermined ignition voltageis determined measuring-technologically and in that affecting the gaspressure and/or the triggering action is realized taking into accountthe measured results. When the regulating action is performed within thecontext of continuous control, the gas pressure or a triggering delay isemployed as a parameter. In this way, the desired ignition delay can beachieved or monitored measuring-technologically.

It is also possible to carry out the method such that the point in timeof ignition is determined measuring-technologically. In this way it ispossible to determine the time which elapses between the point ofreaching the ignition voltage and the effective point in time ofignition; this time corresponds to the ignition delay.

For performing the measuring-technologically determination of the pointin time of ignition, the method can be performed such that the point intime of ignition is measured by means of a measurement of a voltagedifferential of the electrode voltage and/or by means of a measurementof a current differential of the electrode current. At the beginning ofignition, the voltage supplied to the electrodes changes abruptly and,likewise, the current flowing during discharge. The voltage collapsesand the current increases; both can be reliably detected.

The ignition delay can be controlled in that the time between reachingthe predetermined ignition voltage and the point in time of ignition ismeasured and in that the gas pressure is adjusted based on the measuredresults in order to match the predetermined ignition delay. The timebetween reaching the predetermined ignition voltage and the point intime of ignition is measured, for example, analog by means of anintegrator or digitally by means of a counter. The time is supplied to agovernor as a measured parameter; the governor adjust accordingly thegas pressure in the sense of a stabilization of the ignition delay. Aseries of discharge processes can be averaged, i.e., across a certainnumber of pulses.

A special method is characterized in that a measuring-technologicaldetermination of the voltage present at the electrodes is realized fromthe beginning of the voltage increase across a certain time intervalthat includes a presumed point in time of ignition, wherein, for themeasuring-technological determination, preferably an ignition voltageintegrator is used. The time interval therefore surpasses the durationthat is required for the charging process or the voltage increase at theelectrodes. As a result of this, information in regard to the ignitionvoltage and in regard to the ignition delay can be derived from the samesignal. The ignition voltage integrator enables a variety of informationbased on the same measured signal.

Moreover, the method can be modified such that a measuring-technologicaldetermination of the voltage present at the electrodes includes savingthe reached ignition voltage value up to the point of beginning of thesubsequent voltage increase. The saving action is realized, for example,by means of a sample-and-hold circuit.

Expediently, the method can be carried out such that the charge state ofthe capacitor block connected directly to the electrodes as an energystorage device is monitored continuously during voltage increase andthat, after reaching a predetermined ignition voltage, triggering iscarried out, as needed with a predetermined triggering delay.Information in regard to the charge state of the capacitor block can beobtained and evaluated with a suitable electronic device. Theinformation is the basis for enabling operation of the method accordingto the above described strategies wherein influence is exerted on thegas pressure and/or the triggering of a triggering pulse.

In some high-voltage capacitors their capacitance depends greatly on thetemperature. In such cases, care must be taken that the energy of thecapacitor at the time of ignition is maintained constant. In thisconnection, it is not important to maintain a constant ignition voltage;instead, the predetermined ignition voltage must be corrected byperforming a corrective computation. For such a corrective computationthe temperature of the capacitor or the capacitance across the durationof the charge ramp or the supplied charge voltage can be measured inorder to carry out a corresponding correction.

A special method is characterized in that triggering is carried out bymeans of a triggering electrode acting on charge carriers of anintermediate electrode space in that its blocking potential providedrelative to a cathode is reduced. In this way, a triggering pulse can bereached at a predetermined point in time in order to influence in thisway the ignition delay.

In regard to a high EUV light efficiency, the method can be carried outsuch that the energy storage device is charged until a predeterminedignition voltage has been reached while forgoing complete recombinationof the plasma taking place after extinguishing of the plasma. In thisway, especially the repetition frequency can be increased, wherein theenergy storage device can be recharged within shorter time intervals.

In this connection, it is also possible to allow a high-impedance plasmato burn between the electrodes in the time period between two plasmadischarges provided for generating radiation. The high-impedance plasmaresults in improved conditions for a starting plasma of high currentdischarge.

The supply of stored energy into a discharge operated by automaticfiring is carried out at the time of firing, i.e., automatically withthe ignition of the plasma. However, in this connection it must be takeninto consideration that a discharge system without triggering has only asingle firing point that is determined by the conditions of the Paschencurve. This point is not stable. When the electrode system is heated inparticular within the discharge chamber, the firing will no longer takeplace at the same voltage.

Moreover, firings will repeat themselves in fast sequence to thusgenerate radiation constantly. Between two firings the system requires acertain amount of time for recombination of the gas in the dischargechamber. During this time period, the gas returns, at least partially,into its initial state so that the energy storage device can again berecharged and the required voltage can be build up at its electrodes. Asa result of this, the state of the system also depends on when the lastfiring has taken place, i.e., at which repetition frequency thegeneration of the radiation has been carried out. At a high repetitionfrequency, the working point positioned on the Paschen curve will bedifferent than for a low repetition frequency. In practice, this meansthat the repetition frequency can be very limited because no stableworking point can be found at all anymore. In connection with this,problems reside in that it is not possible to switch quickly enough fromone repetition frequency to another and that even for a certainrepetition frequency switching on and off cannot be carried outrepeatedly. Switching on and switching off is particularly importantwhen a lithography device is operated where between the exposureprocesses pauses are mandatory in order to be able to performadjustments on the device.

The invention therefore has additionally the object to improve a methodfor generating extreme ultraviolet radiation and soft x-ray radiationwith a gas discharge operated on the left branch of the Paschen curve,in particular, for EUV lithography, wherein a discharge chamber of apredetermined gas pressure and two electrodes are used, wherein theelectrodes have an opening, respectively, positioned on the samesymmetry axis and, in the course of a voltage increase upon reaching apredetermined ignition voltage, generate a plasma located in the areabetween their openings, which plasma is a source of the radiation to begenerated, wherein an ignition of the plasma is realized by triggering,and wherein with the ignition of the plasma an energy storage devicesupplies by means of the electrodes stored energy into the plasma, suchthat for a method performed by pulse operation for the generation of theEUV light a precise control of the pulses can be achieved, inparticular, within a wide parameter field of the discharge processes, inorder to improve in this way the radiation yield of the EUV light in thesense of the afore described object.

This object is solved in that the ignition of the plasma is realized bya triggering electrode whose potential before beginning the triggeringprocess is higher than that of one of the electrodes used as a cathode.

By the triggering action, an influence is exerted onto the ignitionconditions for the plasma. In particular, triggering affects thedistribution of charge carriers in the ignition area of the plasma andthus also the point in time at which the ignition will effectivelyoccur. In this connection, the potential of the triggering electrodebefore the beginning of the triggering process is higher than that ofthe cathode. As a result of this, an effect on the field generation inthe discharge chamber is realized in such a way that no firing canoccur. Firing is possible only when the potential that prevents firingis removed.

In a special way, the method is carried out such that a voltage of thetriggering electrode relative to the electrode that is used as acathode, the voltage on both electrodes, and the gas pressure of thedischarge chamber are adjusted such that upon supplying the triggeringvoltage ignition of the plasma will not occur and will occur only afterswitching off the triggering voltage. Switching off the triggeringvoltage enables such a generation of the electrical field in thedischarge chamber that the firing conditions are fulfilled. The point intime of firing can be precisely determined by the triggering signal,i.e., by switching off the triggering voltage. It is important in thisconnection that the parameter range for a discharge can be significantlybroadened. The pressure in the gas chamber, the spacing of theelectrodes, and the voltage at the electrodes can be selecteddifferently as a function of the triggering voltage. While the firing inthe un-triggered case is determined only by a single point on thePaschen curve, in the triggered case large voltage ranges ΔU or pressureranges ΔP can be determined in which, after the triggering pulse, firingoccurs.

It is possible to adjust the parameters such that the method is operatedwith repetition frequencies between >0 Hz and 100 kHz. Good results werefound for repetition frequencies of 10 kHz.

Moreover, it is possible to perform the method such that it is operatedwith long operating intervals that are adjustable by switching on andoff; during the intervals a fixed repetition frequency is used. Anoperating interval begins with switching on and ends with switching off.During an operating interval, for example, one wafer is exposed in apartial area. The radiation which is responsible for exposure is carriedout according to one of the above described methods, in particular, at afixed repetition frequency. After completion of an operating interval,an adjustment of the exposure device and/or of the wafer can be realizedin order to then repeat, after exposure of the same wafer or of adifferent wafer, the described method with a predetermined repetitionfrequency.

The invention relates also to a device for generating extremeultraviolet radiation and soft x-ray radiation with a gas dischargeoperated on the left branch of the Paschen curve, comprising a dischargechamber of a predetermined gas pressure and two electrodes, wherein theelectrodes have an opening, respectively, positioned on the samesymmetry axis and, in the course of a voltage increase upon reaching apredetermined ignition voltage generate a plasma located in the areabetween their openings, which plasma is a source of the radiation to begenerated, comprising a triggering electrode in the space adjoining thefirst electrode for triggering an ignition of the plasma, in particularfor performing the method described above. Such a device is to beimproved in particular for performing the above described methods suchthat a high service life and excellent cooling action of the electrodesis ensured. The above described object is solved in that the triggeringelectrode is embodied as a wall which has at least over surface areaportions thereof has a predetermined spacing from the opening of thefirst electrode. The configuration of the triggering electrode as a wallensures also in the case of a temperature-caused and plasma-caused wearof material a long durability and its large surfaces can be cooledeasily, which, in turn, is beneficial with regard to a long servicelife. At the same time, the arrangement of the triggering electrode at apredetermined spacing from the opening of the first electrode ensuresthat the shape of the electrical field required for the field generationis ensured by means of the first electrode.

In the above sense it is advantageous to configure the device such thatthe first electrode is a hollow electrode and that the triggeringelectrode is a wall or wall section within the geometry of this hollowelectrode. This provides a corresponding simplification of the electrodeconfiguration.

When the triggering electrode is configured as a back wall that isparallel to the hollow electrode and positioned opposite its opening,the simplification of the electrode configuration is particularlyenhanced. In particular, with regard to the symmetry axis of the boresof the electrode symmetrical configurations of the electrode systems canbe achieved.

It is preferred that the triggering electrode has a through openingarranged on the symmetry axis. In this way, it can be prevented thatparticle radiation that occurs upon discharge and the connected pulsedcurrents of typically a few 10 ampere can flow undesirably via thetriggering electrode to the electronic triggering device.

For the configuration of a hollow electrode it is advantageous toconfigure the device such that the triggering electrode is cup-shapedand that a cup axis extending perpendicularly to the cup bottomcoincides with the symmetry axis of the electrodes.

A simplified configuration results when the triggering electrode ismounted by means of an insulating device on the first electrode. Theinsulating device makes it possible that the first electrode, on the onehand, and the triggering electrode, on the other hand, are maintained atdifferent electrical potentials.

The afore describe configuration of the device can be specified in thatthe first electrode has an annular collar that is concentric to itsopening and adjoins the triggering electrode while overlapping theinsulator or engages an annular recess of the triggering electrode whilemaintaining a potential-separating spacing in each case. In this way,vapor deposition and short-circuiting of the insulator can be prevented.

The invention relates also to a device for generating extremeultraviolet radiation and soft x-ray radiation with a gas dischargeoperated on the left branch of the Paschen curve, comprising a dischargechamber of a predetermined gas pressure and two electrodes, wherein theelectrodes have an opening, respectively, positioned on the samesymmetry axis and, in the course of a voltage increase upon reaching apredetermined ignition voltage, generate a plasma located in the areabetween their openings, which plasma is a source of the radiation to begenerated, comprising a triggering electrode in the space adjoining thefirst electrode for triggering an ignition of the plasma, and comprisingan energy storage device for supplying stored energy into the plasma viathe electrodes, in particular for performing the afore described method.In such a device ionization can occur in the discharge chamber. Themovable ions located in the electrical field impact on the triggeringelectrode and have generally a sufficiently great energy in order toknock secondary electrons out of the metallic surface of the electrodes.These electrons reach the anode because of the potential difference. Asa result of this, between the anode and the triggering electrode aconducting channel can be formed without the desired firing havingalready occurred in the area of the openings of the electrodes. In thisconnection, a noticeable proportion of the energy storage device can bedischarged by means of the triggering circuit; this entails the risk ofdestruction of such a circuit.

Moreover, a problem can be caused in that the potential of thetriggering electrode, as a result of the formation of a conductingchannel, drops to the level of the anode so that relative to the cathodea higher voltage is generated. As a result of this, undesirabledischarges between the cathode and the triggering electrode can occurwhich can also have a disruptive effect on the proper function of thedevice.

Finally, an ion or particle beam can lead to at least a portion of thecathode being vaporized as a result of its high energy. This results inan undesirable wear and in deposits of vaporized particles on thesurrounding surfaces.

In contrast to this, the invention has the object to configure a devicehaving the aforementioned features such that a high service life withoutdisruptions of its function can be obtained.

The aforementioned object is solved in that the triggering electrode isarranged outside of a particle beam being formed on the symmetry axis orhas to shielding preventing the latter. When the triggering electrode isarranged outside of the particle beam forming along the symmetry axis,the particles or ions accelerated on this axis no longer impact on thetriggering electrode. The afore described malfunctions are at leastsignificantly reduced. The same holds true when the triggering electrodehas a shielding which prevents the generation of a conducting channelbetween the triggering electrode and the anode.

An advantageous configuration of the device is characterized in that thetriggering electrode is arranged on the symmetry axis of the openings ofthe electrodes and in that an end face facing the openings is providedwith an insulator as a shielding at least in the formation area of theparticle beam. The arrangement of the triggering electrode on thesymmetry axis can be such that a uniform influence on the field lines inthe discharge chamber is safely achieved. The insulator provides thedesired protection for the triggering electrode without distorting thefield lines in the discharge chamber in a significant way.

It is advantageous when the insulator is in the form of a layer that isapplied onto the end face of the triggering electrode. The triggeringelectrode in this case is protected sufficiently with a minimal materialexpenditure.

The device can also be configured such that the insulator is formed as amember that is sunk into the end face of the triggering electrode. Inthis case, the triggering electrode and the insulator are to beassembled with conventional mechanical manufacturing means.

An advantageous configuration of the device can be characterized in thatthe insulator has a recess with a cross-section matched to that of theparticle beam. A particle beam, in this case, can impact on the bottomof the recess. The resulting vaporization products deposit thereforemainly on the inner walls of the recess and therefore hardly disturb theother surfaces of the arrangement.

When the recess of the insulator tapers conically, the energy of an ionbeam is distributed onto a larger surface area and, in this way, thelocal thermal heating is reduced. Correspondingly fewer vaporizationproducts are formed.

A further possibility reside in configuring the device such that thetriggering electrode is insulated completely eat least relative to thespace which adjoins the first electrode. The manufacture of thetriggering electrode for such a device can be influenced advantageouslyby a complete insulation or coating. Also, inhomogeneities in regard tothe field formation or discharge formation on the metal surfaces of thetriggering electrode in the transition area between insulated andnon-insulated metal surfaces are eliminated.

A disadvantage of a complete installation of the triggering electrodecan be that under certain discharge conditions electrical charges willcollect on the insulated surface and can effect shielding of thetriggering potential. In order to prevent this, the device can beconfigured such that the shielding of the triggering electrode has aresidual conductivity that dissipates surface charges but prevents adischarge-affecting current flow between the second electrode and thetriggering electrode. In this case of a shielding that dissipatessurface charges, it is advantageous to insulate the triggering electrodecompletely in order to prevent additional dissipation paths.

When the triggering electrode is not to be positioned on the symmetryaxis, it is preferred to configure the device such that the triggeringelectrode is a hollow cylinder surrounding the symmetry axis.

In particular, the device can be configured such that ahollow-cylindrical triggering electrode has a bottom facing away fromthe two electrodes wherein the bottom is configured as an insulator orhas a metal bottom that is connected to the potential of one of theelectrodes and, for this purpose, is insulated relative to thetriggering electrode. The insulator can then take over the functions ofthe afore described insulators, in particular, relative to a possibleparticle beam. When the bottom is a metal bottom, it can either beconnected to the potential of the anode so that a conducting channelcannot result because of identical potentials; however, the metal bottomcan also be connected to the potential of the cathode in order to removeproduced charge carriers.

Moreover, it is advantageous to configure the device such that thetriggering electrode is an annular plate or at least an electrode pinwhich is/are mounted transversely to the symmetry axis of the electrodesin the first electrode. With the annular plate or with the electrodepin, the electrical field can be affected in the discharge chamber or inthe space adjoining the triggering electrode in order to influence thedischarge behavior of the device. In order to reach the afore describedgoal, the triggering electrode is mounted in an insulated way within thefirst electrode.

The device is exposed during its function to significant heatdevelopment. It is therefore expedient to configure it such that theshielding is comprised of temperature-resistant insulation material.

Because of the described heat development, it is also expedient toconnect the shielding with the triggering electrode in a thermally wellconducting way in order to dissipate heat.

In order to intercept the predominant portion of the charge carriersthat reached the shielding the area of the symmetry axis, the device isexpediently configured such that the shielding has a diameter thatcorresponds at least to the diameter of the openings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained with the aid of a drawing. It is shownin:

FIG. 1 a schematic illustration of an electrode system;

FIG. 2 FIG. 3 diagrammatic illustrations of the voltage course at theelectrodes of the electrode system for an ignition process of a plasmaduring pulse operations;

FIG. 4 FIG. 5 differently embodied electrode configurations;

FIG. 6 a schematic illustration of an electrode system, similar to FIG.1;

FIG. 7 a diagram-like illustration of the dependency of the ignitionvoltage of an electrode system from the pressure in a discharge chamber;and

FIG. 8 through 18 schematic illustrations of the electrode systems withdifferently configured triggering devices.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows schematically the configuration of an electrode systemarranged in a discharge chamber 10. The discharge chamber 10 is filledwith a gas of a predetermined gas pressure and can be formed by suitablyconfigured electrodes of the electrode system itself. The gas pressureis adjustable. The devices of the discharge vessel for adjusting the gaspressure and a configuration of the electrode system matched thereto ispresent but is not illustrated.

Two electrodes 11, 12 are present. The electrode 12 is configured as ananode with a central opening 15 which conically widens starting at anintermediate electrode space 22.

The electrode 11 is a cathode, in particular, a hollow cathode with acavity 23 that is connected by means of an opening 14 of the cathode tothe intermediate electrode space 22. The openings 14, 15 are alignedwith one another and define an axis of symmetry 13 of the electrodesystem. The electrodes 11, 12 are insulated relative to one another. Aninsulator 29 serving for this purpose determines the electrode spacing.

As a result of the described configuration, the electrode system isenabled to form field lines upon supplying an electrical high voltage inthe range of, for example, several 10 kV, wherein the field lines, atleast in the area of the intermediate electrode space 22, are straightand parallel to the axis of symmetry 13. When the voltage is increasedstarting from a predetermined low value in a pulsed fashion, thereresults a charge ramp or voltage increase 16 according to FIGS. 2, 3.Ionization processes occur that, as a result of the field strengthconditions, are concentrated in the intermediate electrode space 22. Forthis purpose, the voltage increase 16 and the gas pressure are adjustedrelative to one another such that, because of the ionization, a gasdischarge on the left branch of the Paschen curve results where a plasmachannel or its plasma is not generated by means of a single short-termelectrode avalanche but in several steps by means of secondaryionization processes. As a result of this, the plasma distributionalready in the starting phase is highly cylindrically symmetrical, as isillustrated in the schematic illustration of the plasma in FIG. 1. Theresulting plasma 17 is a source for the radiation 17′ to be generated.

It is understood that an ignition of the plasma 17 is possible only whenan ignition voltage U_(z) has been reached. According to the invention,it is provided that an ignition delay 18 occurs. As a result of this,the point in time of ignition t_(z) despite the presence of the ignitionvoltage U_(z) is correspondingly delayed. The magnitude of the ignitiondelay 18 is regulated by controlling the gas pressure. The magnitude ofthe ignition delay is within typical durations in the range of severalmicroseconds up to a few milliseconds. The ignition delay results in aprolongation of the generation of the conductive plasma. In this way, animprovement of the cylinder symmetry of the plasma 17 is achieved.

The plasma which is formed after the ignition delay can be referred toas a starting plasma. It can serve for energy introduction from anenergy storage device during automatic firing operation. FIG. 1 showsthe capacitor block 21 as an energy storage device; upon reaching thepredetermined ignition voltage and ignition delay the energy storagedevice will discharge and, in this way, enables the introduction ofcurrent pulses within a two-digit kilo ampere range into the plasma. Theresulting Lorentz forces of the magnetic field constrict the plasma sothat a high luminance results and, in particular, extreme ultravioletradiation and soft x-ray radiation are generated which in particularhave the required wavelength for EUV lithography.

Instead of influencing the ignition delay 18 by means of the gaspressure, in addition a triggering electrode can be used for affectingthe ignition delay. By means of a triggering electrode 19 it can beachieved that, despite reaching a predetermined ignition voltage U_(z),a firing for discharge between the electrode 11, 12 will not yet takeplace. A triggering delay 20, achievable with the triggering electrode19 according to FIGS. 4, 5, is illustrated in FIG. 3. It is added to theignition delay 18. Affecting the total ignition delay by means of atriggering delay 20 is particularly advantageous because it is possibleto employ measuring technology in order to reach the precise point intime of ignition t_(z). This holds true for the case where the gasdischarge operation is carried out with automated firing as well aswhere a switching element between the electrode system and the capacitorblock is used. The switching element makes it possible to supply avoltage to the electrode system which is greater than the ignitionvoltage U_(z) required for the automatic firing operation. In the lattercase, it is possible to work at higher gas pressures; this results inhigher intensities of the emitted radiation.

It is expedient to measure the ignition point, in particular, when bymeans of the, charge device a higher voltage is allowed at the electrodesystem than their predetermined ignition voltage. The voltage which isconnected to the electrode system, i.e., the course of a voltageincrease 16, can be detected, for example, by determining the temporalchange of the voltage supplied to the electrodes 11, 12. Accordingly, adU/dt measurement is carried out. It is also possible to carry out adl/dt measurement, i.e., a detection of the temporal change of thedischarge current. Current and voltage change suddenly upon reaching theignition point t_(z). The time between reaching the predeterminedignition voltage U_(z) and the point in time of ignition can bemeasured, for example, in an analog fashion by means of an integrator ordigitally by means of a counter. This time is supplied as a measuredvalue to a controller which affects accordingly the gas pressure in thesense of stabilization of the ignition delay 18. This holds true alsofor the situation of application of a triggering delay 20.

The measurement can be performed, for example, by means of an ignitionvoltage integrator which takes over processing of the measured valuehigh voltage or voltage at the electrode system or the capacitor blockwhich processing is upstream of the actual controller. In thisconnection, the ignition voltage integrator integrates the high-voltagesupply to the electrodes 11, 12 that is divided down and registers theirfinal value by means of a sample-and-hold until the next charge process.The integration process begins with the charging process, i.e., with theincrease of the electrical voltage supplied to the electrodes 11, 12 andis continued for a duration that is determined by a timer. This durationis generally longer than the actual charging process so that in this wayalso the desired information with regard to the magnitude of theignition delay can be determined. Additional non-linear members such as,for example, square-root law transfer elements, can be used in order toimprove the transmission characteristic line. In this way, informationwith regard to the ignition delay are obtained as well as with regard tothe ignition voltage, and this with the same measured signal. Incontrast to a peak detector that determines the ignition voltage, themethod is entirely unsusceptible with regard to disturbance peaks thatcan result, for example, from high-voltage generators. An electronicdevice is not required for the ignition point detection.

If the method is carried out without triggering electrode, the ignitionpoint t_(z) can be determined only via the magnitude of the gaspressure. In a method with triggering electrode the afore describedtriggering delay can be used in order to determine the point ofignition, if needed, in combination with a selection of a suitable gaspressure. In this way, the charge state of the capacitor block 21 isdetermined by means of an electronic evaluation device, for example, bymeans of the above described ignition voltage integrator. Triggering bymeans of the triggering electrode results in that, despite reaching theignition voltage U_(z) a plasma deformation causing the discharge of thecapacitor block 21 will not yet take place. Only in the case oftriggering ignition occurs, i.e., in the case of triggering a triggeringpulse after the predetermined triggering delay 20. The controllingparameter can be also the gas pressure which, for example, is adjustedby means of an electronic inlet valve. When the maintenance voltage isnot reached after a predetermined reading time, the gas pressure must bereduced. In the other situation, the gas pressure, when ignition doesnot occur, must be increased after the triggering pulse. A controlparameter in this method employing a triggering electrode is in the endthe ignition delay, i.e., the time between triggering the triggeringpulse and the voltage collapse. The pressure is then adjusted such thatthe ignition delay is maintained constant within certain tolerances.

The triggering delay 20 indicated in FIG. 3 is provided in an exemplaryfashion relative to the point in time of reaching the predeterminedignition voltage U_(z). In principle, any point in time can be selectedprior to this and can be determined by a suitable electronic device; forexample, the beginning of the charging process or reaching of apredetermined value of the charge voltage can be selected.

In FIGS. 4, 5, for example, configurations of triggering electrodes areillustrated.

The triggering electrodes 19 are adjacent to the cathode 11 on the sideof the cathode facing away from the anode 12. In the illustratedembodiments, they are assembled by means of an insulator 26 togetherwith the cathode 11, wherein means for holding together the electrode11, the insulator 26, and the triggering electrode 19 are notillustrated.

All embodiments of the triggering electrode have in common that,relative to the symmetry axis 13, they are symmetrically arranged. Allembodiments have an axis that is aligned with the symmetry axis 13. Inthis connection, the triggering electrode 19 is configured as a wall orwall section. It is positioned at a predetermined spacing away from theopening 14 of the electrode 11. In this way, it can be achieved at thesame time that the electrode 11 is configured as a hollow electrode, forexample, as a hollow cathode. The triggering electrode 19 then formsessentially the back wall of the cathode. Such a back wall is the wall29 in the embodiment of FIG. 4 and a cup bottom 19′ of the cup-shapedtriggering electrode 19 in the embodiment of FIG. 5.

The cup-shaped configuration of the triggering electrode 19 shows thatit cannot only be the back wall of the electrode 11 but also thesidewall of the space 23 of this hollow electrode that is to beenclosed. It is also conceivable that the triggering electrode 19 isexclusively a sidewall section of an electrode 11 which is connected, bythe way, to the electrode potential or the cathode potential.

FIG. 4 illustrates that the triggering electrode 19 is provided with athrough opening 24 which serves for passage of the particle beams thatform in accordance with the electrode configuration primarily in thearea of the symmetry axis. With such a penetration opening, loading ofthe electronic triggering device can be maintained within acceptablelimits. The particle beams are received by the parts of the electrodesystem which are connected to the potential of the cathode. A throughopening 24 can also be used in the case of FIG. 5.

In FIG. 4, bores 24′ that are parallel to the through opening 24 areprovided. The bores 24′ can be gas bores, i.e., for passage of gas inthe sense of a gas inlet. The through opening 24 can also be used in thesense of such a gas passage or in the sense of a gas inlet. Both isparticularly advantageous when the electrode system itself forms thedischarge chamber 10.

In the case of gas discharge projecting into the space 23, vapordeposition on the insulator 26 with metal vapor is to be expected. Thiscould lead to shortcircuiting of the insulator 26. In order to shieldingit against the occurring metal vapor, the electrode 11 is provided withan annular collar 27 which is arranged concentrically to the opening 14and which overlaps the torus-shaped insulator 26. Moreover, thetriggering electrode 19 is provided with an annular recess 28. Theannular collar 27 engages the annular recess 28. In this way, apotential separating spacing is provided which, however, must be onlysmall because of the usually minimal potential differences between thecathode 11 and the triggering electrode 19.

The triggering electrodes according to FIGS. 4, 5 are possible also inconnection with a hollow anode. In this case, the light of the plasma 17would have to be decoupled from the electrode 11 or from the hollowcathode. However, it is advantageous to decouple the light at the anode,as illustrated in FIG. 1, and to operate the cathode with negative highvoltage because, in this way, debris from sputtering and high frequencydischarges are prevented better in the part of the electrode systemfacing an observer.

The potential of the triggering electrode 19 is selected beforetriggering a triggering pulse and thus before triggering a low-impedanceplasma discharge such that the charge carriers are removed from thehollow electrode or hollow cathode and the intermediate electrode spacein the bore hole area. This is realized, for example, by supplying tothe triggering electrode 19 a positive voltage of typically several 100V relative to the cathode potential. A triggering pulse is triggeredwhen the potential of the triggering electrode is reduced to that of thecathode or in that a negative potential is supplied to the triggeringelectrode 19. Typical constant time values for a change of the potentialof the triggering electrode 19 are advantageously in the range of a fewnanoseconds up to several 100 ns.

In order to obtain high light efficiencies, it is desired to enable arepetition frequency of the discharges that is as high as possible,i.e., in the range of several kHz and preferably above 10 kHz. In thisconnection, the required resolidification or recombination times of theplasma set limits. These limits depend on the type of gas with which themethod is operated. With regard to a high radiation efficiency in theEUV field, the application of xenon is of particular interest. Whenoperating with pure xenon, the repetition frequencies aboveapproximately 1 kHz for typical pulse energies in the range of 1 Jouleup to 10 Joule in operation with automatic firing can hardly be reached.It is therefore desirable to perform measures for accelerating theresolidification.

As one possibility the admixture of gases should be mentioned. A fastrecombination of the plasma after discharge of the capacitor block canbe achieved by admixing gases, for example, air, synthetic air,nitrogen, oxygen, or halogens.

Moreover, the transport of charged particles away from the area of theopenings 14, 15 can be enhanced by suitable gas flow. A flow with gasinlet via the cathode and/or via the intermediate electrode space andwith gas evacuation via the anode, which according to FIG. 1 is theelectrode facing the observer, is advantageous. With such a gas flow apressure drop in the area of the anode or in the area of a hollow anodecan be produced. By means of such pressure gradients it is possible tomove the plasma 17 in order to achieve an increased transmission for theEUV radiation in the observation path up to the user.

Further measures for increasing the repetition frequency can beperformed in connection with the capacitor block 21. This is based onthat the generation of the low-impedance plasma, depending on theconditions, takes up to several 100 microseconds. The capacitor block 21can now be charged faster than the generation time of the low-impedanceplasma. As a result of this, a complete recombination of the plasma canbe forgone. It is moreover also possible to allow a high-impedanceplasma to burn between two discharges in the area of the openings 14,15; this results in better conditions for a starting plasma of the highcurrent discharge.

FIG. 6 shows schematically the configuration of an electrode systemarranged within the discharge chamber 10. The discharge chamber 10 isfilled with a gas having a predetermined gas pressure and can be formedby suitably designed electrodes of the electrode system itself. The gaspressure is adjustable. The devices for adjusting the gas pressure ofthe discharge vessel 10 and a configuration of the electrode systemmatched thereto are present but not illustrated.

Two electrodes 11, 12 are present. The electrode 12 is an anode with acentral opening 15 and widens conically starting at an intermediateelectrode space 22.

The electrode 11 is a cathode and is embodied as a hollow cathode with acavity 23 connected by means of the opening 14 of the cathode to theintermediate electrode space 22. The openings 14, 15 are aligned andtogether form a symmetry axis 13 of the electrode system. The electrodes11, 12 are insulated relative to one another. An insulator 29 servingfor this purpose determines the electrode spacing.

The electrode system is enabled as a result of the afore describeconfiguration to generate filed lines upon supplying an electrical highvoltage in the range of, for example, several 10 kV; the field linesextended at least in the area of the intermediate electrode space 22 instraight lines in parallel to the axis of symmetry 13. When the voltageis increased starting from a predetermined low value in a pulsedfashion, a charge ramp or voltage increase results. This causesionization processes which are concentrated because of the fieldstrength conditions within the intermediate electrode space 22. For thispurpose, the voltage increase and the gas pressure are adjusted relativeto one another such that as a result of the ionization gas discharge onthe left branch of the Paschen curve will result, wherein a plasmachannel or its plasma is not generated by a single short-time electrodeavalanche but in several steps by means of secondary ionizationprocesses. As a result of this, the plasma distribution already in thestarting phase is highly cylindrical-symmetrical, as schematicallyillustrated in FIG. 6. The generated plasma 17 is a source of theradiation 17′, an electron radiation, that is to be generated.

The generated plasma can be referred to as a starting plasma. It canserve for energy coupling from an energy storage device for automaticfiring operation. FIG. 6 shows a capacitor block 21 as an energy storagedevice which discharges after reaching the predetermined ignitionvoltage and, in this way, enables a supply of current pulses within atwo-digit kilo ampere range into the plasma. The Lorentz forces of themagnetic field which are formed accordingly constrict the plasma so thata high light efficiency results and, in particular, extreme ultravioletradiation and soft x-ray radiation are is generated having, inparticular, the required wavelength for EUV lithography.

The electrode system illustrated in FIG. 6 is provided with a triggeringdevice in the area of the electrode 11. For this purpose, the electrode11 has a triggering electrode 19 on the symmetry axis 13 that is securedby an insulator 26 in the bottom 30 of the electrode 11. The insulator26 serves for providing a potential to the triggering electrode 19 thatis different from that of the electrode 11. In this connection, thetriggering electrode 19 has a parasite capacitance 31 relative to theelectrode 11, measured parallel to a switch 32 with which bothelectrodes 19, 11 can be connected to the same potential.

Conventionally, the electrode 12 is configured as an anode and isgrounded, as illustrated. In contrast, the cathode is connected to anegative potential −V while the triggering electron 19 is connected to apotential −V+V_(t). The potential of the triggering electrode beforebeginning the triggering process is thus somewhat higher than that ofthe electrode 11. For the purpose of triggering, a triggering pulse istriggered by closing the switch 32, and the potential of the triggeringelectrode 19 is dropped to that of the electrode 11. Typical constanttime values for a change of the potential of the triggering electrode 19are advantageously in the range of a few nanoseconds s up to severalhundred nanoseconds.

The electrode arrangement schematically illustrated in FIG. 6 istypically configured such that between the electrodes 11, 12 a spacingof 1 to 10 mm is present. The smallest passage of the openings 14, 15 istypically 1 to 10 mm. The volume of the space 23 in the electrode 11configured as a hollow cathode is typically 1 to 10 ccm. The gaspressure is between 0.01 and 1 mbar. The electrode voltage is typically3 to 30 kV, and the potential difference between the triggeringelectrode 19 and the electrode 11 is between 50 V and 1,000 V.

Principally, the ignition voltage at which firing between the electrodes11, 12 occurs and the pressure depend form one another in accordancewith the curve illustrated in FIG. 7. FIG. 7 relates to the left branchof the Paschen curve.

The left curve of FIG. 7 applies to the operation of un-triggereddevice. On this curve for V=0 6 there exists only a single firing pointwhich is, for example, provided at a gas pressure of 7 Pa atapproximately 8 kV. Other pressures in the space 23 have correspondinglydifferent ignition voltages. The triggering voltage, i.e., the potentialdifference between the triggering electrode 19 and the electrode 1 canhowever also deviate from 0. In this case, V_(t) is not equal 0 but, forexample, equal V₁ or V₂. As a result of this, with the suitable value ofthe triggering voltage V_(t) it can be achieved that the device can beoperated with different parameters. For a predetermined voltage at theelectrodes 11, 12 there is the possibility of pressure variations asillustrated in FIG. 7. In a similar way, for a certain pressure thevoltage variations illustrated in FIG. 2 are possible. Correspondingly,also the point in time of firing can be determined precisely by means ofthe triggering signal without reaching a working area where the abovedescribed difficulties would occur. In particular, repetition frequencycan be ensured as they are required for the necessary use, for example,in the range of 10 to 22 Hz. Also, operating intervals for certain fixedrepetition frequencies are possible so that between the operatingintervals the energy essentially required for generating the desiredradiation can be saved. The stability of the working point issignificantly improved.

Triggering is achieved by the circuit illustrated in FIG. 6. Thecapacitor block 21 is charged in that the electrode 11 is connected tonegative voltage while the electrode 12 is grounded. The connection ofthe two electrodes 11, 12 is realized by a low-inductive circuit via thecapacitor block 21. A high-impedance circuit connects the triggeringelectrode 19 with the electrode 11 wherein the connection can be openedby the switch 32. In the open situation, a potential difference V_(t)relative to the electrode 11 is present at the triggering electrode 19.For this case, the voltages at the electrodes 11, 12 as well as the gaspressure of the intermediate electrode space or chamber 23 of theelectrode 11 are adjusted such that upon supplying a triggering voltageV_(t) an ignition of the plasma 17 cannot take place. When the switch 32is however closed, the potential difference V_(t) is eliminated and thetriggering electrode 19 is supplied with the potential of the electrode11; a protective resistor 33 protects the voltage source of thetriggering voltage.

When the switch 32 is open, it is however possible that between thetriggering electrode 19 of FIG. 6 and the electrode 12, serving as ananode, a conducting channel with a corresponding particle beam is formedwhich discharges the energy of the capacitor block 21 and can also causedamage of the triggering circuit. In FIGS. 8 through 18 differentlyconfigured triggering electrodes in a schematically illustrated systemof main electrodes 11, 12 are illustrated which can contribute to properfunctioning of the device.

FIGS. 8 to 18 show triggering electrodes 19 arranged coaxially to thesymmetry axis 13 defined by the electrodes 11, 12 or their openings 14,15. In this connection, the triggering electrodes 19 of FIGS. 8 through13 are configured such that they have an end face 34 facing the opening14. At least this end face 34 is provided with a shielding 35 that isdesigned differently, respectively. Each shielding 35 is at least solarge that it matches the diameter of the openings 14, 15. The shielding35 is thus present in the vicinity of the triggering electrode 19 in thegeneration area of the particle beam.

In the case of FIG. 8, the shielding 35 is an insulator in the form of alayer applied to the end face 34 of the triggering electrode 19. In thecase of FIG. 9, the shielding 35 is also embodied as an insulator but itis a member that is sunk into the end face 34 of the triggeringelectrode 39. The cross-section of this member is, for example, of acircular cylindrical shape in order to be inserted in a conventional wayinto a bore of the triggering electrode 19 which is machined into theend face 34. In FIG. 10 and in FIG. 11 the triggering electrode 19 isidentical to that of FIG. 9. However, different shieldings 35 areinserted into its bore. The shielding 35 of FIG. 10 is again acylindrical member that however has a coaxial recess 36 embodied as ablind bore. The diameter of the blind bore is matched to the diameter ofthe potential partial stream. The shielding 35 of FIG. 11 is providedwith a recess 36 which conically tapers away from the openings 14, 15. Aparticle beam that is possibly formed impinges on the relatively largesurfaces of the shielding 35 so that the beam energy is distributed ontoa larger surface area which prevents local thermal heating. In bothcases of FIGS. 10, 11, the recesses are suitable to receive thevaporization products caused by an impinging particle beam whichparticles can deposit on the inner walls of the recesses 36 andtherefore do not disturb the other surfaces of the arrangement.

The triggering electrode of FIGS. 12, 13 are characterized in that theyare completely insulated by their shielding at least relative to thespace 23 adjoining the first electrode 11. The shielding 35 is a coatingwhich does not expose any surface area of the triggering electrode 19.As a result of this, no inhomogeneous electrical fields of any kind canoccur which could to be caused by such exposed spaces. Under certaindischarge conditions, however, it can occur that on the surface of thisshielding 35 electrical charges will collect which can effect shieldingof the triggering voltage. A shielding of the triggering voltage wouldresult in a malfunction of the device. Such a shielding action can beprevented when the shielding 35 is provided with a residual conductivitythat is large enough to neutralize built-up surface charges or todissipate them. This residual conductivity is however not large enoughto allow current flow between the electrode 12 and the triggeringelectrode 19 that significantly discharges the capacitor block 21. FIG.13 shows such a shielding 35 with a suitable residual conductivity.

In all afore described embodiments, the dimensions can be varied withinwide limits. For example, the triggering electrode 19 can be configuredas a thin wire which is coated expediently according to FIGS. 12, 13.

The triggering electrodes 19 of FIGS. 14 to 16 are hollow-cylindrical.These triggering electrodes are arranged coaxially relative to thesymmetry axis 13. As a result of their hollow cylindrical embodiment andthe field generation, on the other hand, a particle beam formed in thearea of the symmetry axis 13 cannot reach the triggering electrode 19and cannot act thereon in a disturbing or destructive way. In FIG. 14the triggering electrode 19 is closed off by a metallic bottom 37 thatis supplied to ground potential and is insulated relative to the hollowcylindrical triggering electrode 19. Between the bottom 37 and theelectrode 12 a particle beam cannot form because this electrode, as ananode, is also connected to ground potential.

FIG. 16 shows a bottom 38 configured as an insulator and therefore has,relative to the particle beam, a similar effect as the shieldingsdescribed in connection with FIGS. 8 to 11. In FIG. 16 the bottom 39 ofthe hollow cylindrical triggering electrode 19 is configured as a mentalelectrode that is conductingly connected to the electrode 11, thecathode. Charge carriers of particle beams present on the symmetry axisare supplied by means of the metallic bottom 39 by a connecting line 40to the electrode 12.

The configurations of FIGS. 17 and 18 are alternative arrangements ofFIG. 16. In all cases, charge particles on the symmetry axis 13 or inthe space 23 are supplied to the electrode 11. In FIG. 17 the triggeringelectrode 19 is embodied as an annular plate. This annular plate ismounted transversely to the symmetry axis 13 of the electrode 11, 12into the first electrode 11. The upper and lower halves thereof,illustrated in FIG. 17, are conductingly connected to by lines 41illustrated in dashed lines and have thus the same potential. Thearrangement of the triggering electrode 19 relative to the symmetry axis13 is cylinder-symmetrical. This is no longer the case in the situationof FIG. 18. In this embodiment, with the exception of the line 41, theconfiguration can be the same as in FIG. 17 in a side view. The symmetryaxis 13, however, is positioned perpendicularly in FIG. 18 relative tothe plane of the illustration, and FIG. 18 shows two identicallyconfigured parts 19′ and 19″ of a triggering electrode that are arrangedcoaxially and transversely to the symmetry axis 13. The parts 19′, 19″represent electrode pins. Instead of the two parts 19, 19′ thetriggering electrode can also be comprised of several parts.

The shieldings 35 employed in connection with the triggering electrodes19 are comprised of temperature-resistant insulation materials, forexample, Al₂O₃, quartz, or silicon carbide. All materials used for theshieldings 35 are connected to the triggering electrode 19 so as toprovide excellent thermal conducting.

Moreover, it is understood that the triggering electrode 19 or its parts19′, 19″ are mounted in an insulated way in the first electrode 11. Theinsulations 42 illustrated in FIGS. 8 through 18 fulfill the samefunctions as the insulator 26 of FIG. 6. The insulation 42 istemperature-resistant, respectively.

1. A device for generating extreme ultraviolet radiation and soft x-rayradiation with a gas discharge operated on the left branch of thePaschen curve, the device comprising: a discharge chamber (10) of apredetermined gas pressure; two electrodes (11, 12) arranged in thedischarge chamber (10), wherein the two electrodes have an opening (14,15), respectively, wherein the openings have coinciding symmetry axes(13); wherein the two electrodes, in the course of a voltage increase(16) upon reaching a predetermined ignition voltage (U_(z)), generate aplasma (17) located in the area between the openings (14, 15); atriggering electrode (19) arranged in a space (23) adjoining a first oneof the electrodes (11), wherein the triggering electrode triggers anignition of the plasma (17) for producing the radiation (17′) by gasdischarge; an energy storage device for supplying stored energy into theplasma (17) with the two electrodes (11, 12); wherein the triggeringelectrode (19) is arranged outside of a particle beam being formed onthe symmetry axes (13) or is provided with a shielding (35) preventingthe particle beam from impinging on the triggering electrode (19). 2.The device according to claim 1, wherein the triggering electrode (19)is arranged on the symmetry axes of the openings (14, 15) of theelectrodes (11, 12), wherein the shielding is an insulator provided onan end face (34) of the triggering electrode facing the openings (14,15) of the electrodes.
 3. The device according to claim 2, wherein theinsulator is a layer applied onto the end face (34) of the triggeringelectrode (19).
 4. The device according to claim 2, wherein theinsulator is a member that is sunk into the end face (34) of thetriggering electrode (19).
 5. The device according to claim 4, whereinthe insulator has a recess (36) with a cross-section matched to theparticle beam.
 6. The device according to claim 5, wherein the recess(36) of the insulator tapers conically.
 7. The device according to claim1, wherein the triggering electrode (19) is completely insulated atleast relative to the space (23) adjoining the first electrode (11). 8.The device according to claim 7, wherein the shielding (35) of thetriggering electrode (19) has a residual conductivity that dissipatessurface charges but prevents a discharge-affecting current flow betweena second one of the two electrodes (12) and the triggering electrode(19).
 9. The device according to claim 8, wherein the triggeringelectrode (19) is formed as a hollow cylinder surrounding the symmetryaxes.
 10. The device according to claim 9, wherein the triggeringelectrode (19) has a bottom that is facing away from the two electrodes(11, 12), wherein the bottom is embodied as an insulator or is embodiedas a metal bottom connected to the potential of one of the electrodes(11, 12) and insulated relative to a remaining part of the triggeringelectrode (19).
 11. The device according to claim 1, wherein thetriggering electrode (19) is an annular plate mounted transversely tothe symmetry axis (13) of the electrodes (11, 12) in the first electrode(11) or the triggering electrode is at least one electrode pin mountedtransversely to the symmetry axis (13) of the electrodes (11, 12) in thefirst electrode (11).
 12. The device according to claim 1, wherein thetriggering electrode (19) is mounted in a first one of the electrodes(11) and is insulated relative to the first electrode.
 13. The deviceaccording to claim 1, wherein the shielding (35) is comprised of atemperature-resistant insulation material.
 14. The device according toclaim 1, wherein the shielding (35) is connected to the triggeringelectrode (19) so as to provide excellent thermal conducting.
 15. Thedevice according to claim 1, wherein the shielding (35) has a diametermatching at least a diameter of the openings (14, 15) of the twoelectrodes.